This application is based upon and claims the benefit of Japanese Patent Application No. 11-326932 filed on Nov. 17, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates generally to a method for manufacturing a semiconductor device, and particularly to a method for manufacturing an SOI (Silicon On Insulator) substrate.
2. Description of the Related Art
In an SOI substrate in which an element formation wafer and a support wafer are bonded together, an SOI layer having a required thickness is provided by polishing a surface of the element formation wafer after bonding the two wafers with an oxide film interposed therebetween. As a conventional polishing method for the SOI substrate, a thickness of the SOI layer is measured after polishing is carried out for a predetermined time, and this polishing and measurement are repeated until the SOI layer has a required thickness. In this method, however, the polishing process must be stopped and the SOI substrate must be detached from a polishing apparatus every time the thickness is measured. Thus, complicated work is required. Besides, because the measurement is not performed continuously, a failure occurrence rate is liable to be increased due to excessive polishing.
The present invention has been made in view of the above problems. An object of the present invention is to provide a method for measuring a thickness of an SOI layer when an SOI substrate is polished.
According to the present invention, when a surface of a semiconductor substrate, which is composed of a first layer and a second layer having different refractive indexes from each other, is polished at a side of the first layer, a thickness of the first layer is measured based on a relation between an intensity and a wavelength of a light that is irradiated to the substrate and is reflected by the substrate at a side of the second layer.
Thus, since the thickness of the first layer can be measured by light irradiated to and reflected from the substrate, the thickness can be measured when the surface of the substrate is polished. The substrate may be an SOI substrate having a semiconductor layer as the first layer and an oxide layer as the second layer.
The surface of the substrate can be polished by a polishing machine that is composed of a wafer support head having an attachment surface for holding the substrate, and a pad that is disposed to face the attachment surface for polishing the SOI substrate. The attachment surface may have a window portion penetrating the wafer support head for allowing the light to be irradiated to the substrate from the side of the wafer support head when the substrate is attached to the attachment surface.